Clinical trials designed to increase cancer preventive service delivery have previously shown modest short term effects. Greater understanding of characteristics of primary care practice that affect response to interventions is needed to discover innovative new strategies for improving practice in a rapidly changing health care environment. This competing continuation study builds on a unique cohort of primary care practices who participated in two prior NCI-funded studies. The Direct Observation of Primary Care Study used a multimethod approach to increase understanding of primary care practice. The ensuing Study To Enhance Prevention by Understanding Practice (STEP-UP) is a clinical trial to improve preventive service delivery in 80 practices. The study's initial intervention (STEP-1) found that an individualized office systems intervention increased delivery of a comprehensive measure of evidence-based preventive services, particularly health habit counseling. Based on preliminary insights from STEP-1, a more comprehensive practice assessment and intervention approach (STEP-2) was developed and implemented in the control (delayed intervention) practices. A unique opportunity for the proposed continuation study is supported by 1) the observation of a highly variable response to intervention, 2) the availability of rich longitudinal data on practices and health systems changes, 3) the availability of unique contextual data from the Center for Studying Health Systems Change and new data from continued assessment of community practices, and 4) the discovery of the relevance of complexity science to understanding primary care practice and health system change. This new study aims to: 1) Develop a comprehensive understanding of factors affecting the response of primary care practices to 2 different quality improvement interventions to increase cancer preventive service delivery rates, and 2) Understand the effect of health care system changes on primary care practices' ability to improve cancer preventive service delivery. This will be accomplished with a multimethod design to create in- depth longitudinal comparative case studies to identify practice and health system characteristics that influence the process of change in response to the interventions. The proposed study will further understanding of features of primary care practices that affect response to quality improvement interventions, and will inform new strategies to increase preventive service delivery.